A 7-YEAR-OLD 11-lb (5-kg) neutered male domestic longhaired cat was presented to its regular veterinarian for vaccinations and a wellness examination. The cat had not received veterinary care in the previous three years. The cat had been vaccinated against rabies and feline viral rhinotracheitis, calicivirus, and panleukopenia at 8 months of age but had not received any vaccinations since then. The results of a feline leukemia virus antigen test had been negative at that time. The owner had adopted the cat when it was 6 weeks old and reported that it had generally been healthy.

The owner expressed concern that the cat had lost weight over the past several months, though the cat had previously been overweight. The cat's appetite seemed unchanged, there were no other systemic signs of disease such as polyuria or polydipsia, and there was no history of inappropriate urination. Multiple cats lived in the household, and they were all housed strictly indoors and fed a commercial feline kibble, but the owner did not closely observe their food consumption and litter box habits.

Initial assessment

On physical examination, the cat's body condition score was 3 (on a scale of 5) with no muscle atrophy. No abnormalities were noted apart from Stage 3 periodontal disease and findings indicative of feline odontoclastic resorptive lesions on the mandibular molars. The cat's weight loss was attributed to probable reluctance to eat because of oral pain. Rabies, feline viral rhinotracheitis, calicivirus, and feline panleukopenia virus vaccinations were given, and the cat was scheduled for a dental examination, radiography, and prophylaxis with extractions as necessary.

Preanesthetic evaluation

Figure 1. Longitudinal ultrasonograms of the right (A) and left (B) kidneys at initial presentation. The normal architecture of the right kidney has been disrupted and appears to be a mass of mixed echogenicity; it is markedly enlarged compared with the normal left kidney.

One week later, the cat was admitted to the clinic for the dental procedures. The results of a preanesthetic complete blood count (CBC) (Table 1) and an activated partial thromboplastin time were normal. A preanesthetic serum chemistry profile revealed one abnormality—a low blood urea nitrogen (BUN) concentration (14.6 mg/dl; reference range = 16 to 36 mg/dl). This abnormality could be caused by decreased protein intake, polyuria and polydipsia, or hepatic insufficiency. In this case, decreased protein intake was considered most likely.

Table 1 Complete Blood Count Results

On physical examination, a cranial abdominal mass was palpated. An abdominal ultrasonographic examination revealed a normal liver, gallbladder, spleen, left kidney, and urinary bladder and normal intestines. The right kidney was markedly enlarged and irregular. The normal renal architecture of the cortex, medulla, and pelvis had been effaced by an irregular mass that had mixed echogenicity (Figure 1). Urinalysis of a sample obtained by cystocentesis revealed marked hematuria, pyuria, and cocci. The urine was submitted for bacterial culture (Table 2). Fine-needle aspirates were obtained from the right kidney with ultrasound guidance and were submitted for cytologic evaluation.